With advancements in technology, faster data transmission rates and increased bandwidth are required. DSL technology has become an important tool in obtaining these requirements. Two different types of DSL applications are symmetric DSL (SDSL) applications and asymmetric DSL (ADSL) applications. Symmetric DSL applications are referred to as symmetric because they offer an inherently symmetric data rate. These applications generally use baseband codes such as 2BIQ, Optis, or Pulse Amplitude Modulation (PAM) that require a transmission of very low frequency signals. Although generally, SDSL applications frequently use a frequency band from low frequency to high frequency such as 80 kilohertz to 1.1 megahertz.
Asymmetric DSL applications are referred to as asymmetric because they offer an inherently non-symmetric data rate. ADSL applications have high data rates from a central office (CO) to a customer premise (CP) and low data rates from the CP to the CO.
Two different kinds of ADSL applications are asymmetric digital subscriber line over plain old telephone service (ADSL over POTS) applications and asymmetric digital subscriber line over integrated services digital network (ADSL over ISDN) applications. In ADSL over POTS applications, both ADSL and POTS services are provided on a single line. Similarly, in ADSL over ISDN applications, both ADSL and ISDN services are provided on the same line.
ADSL applications use pass band line codes that allocate a low frequency band to either POTS or ISDN. These applications do not use part of the frequency band used by POTS or ISDN. POTS uses a frequency band referred to as a voice band ranging approximately from 0 to 4 kilohertz. ISDN applications use a frequency band ranging from a low frequency to approximately 80 kilohertz.
Transceivers for ADSL and SDSL applications currently use different line interface circuits. As an example, transceivers for ADSL applications such as carrier amplitude/phase (CAP) modulation or discrete multi-tone (DMT) based ADSL, rate adaptive DSL (RADSL), currently use different transformers and associated components as compared to transceivers for SDSL applications such as ISDN DSL (IDSL), High-bit-rate DSL (HDSL), HDSL2, and single-pair high-bit-rate DSL (SHDSL). The use of different transformers and associated components requires more board space, is more expensive to install at the CO, and the CP can handle either ADSL or SDSL applications but not both. Hence, an unaddressed need exists in the industry for a unified DSL transceiver that can be integrated on a board, reduce the cost of installing and maintaining the various kinds of DSL services at the CO, and that can handle all types of DSL services at the CP.